In a fuel injection control system of an internal combustion engine, a required injection quantity is calculated according to an operating state of the internal combustion engine and a fuel injector is opened by an injection pulse of a pulse width corresponding to the required injection quantity to thereby inject fuel of the required injection quantity.
In the fuel injector of an internal combustion engine of a direct injection type in which the fuel of high pressure is injected into a cylinder, as shown in FIG. 3, the linearity of a change characteristic of an actual injection quantity with respect to an injection pulse width tends to be worse in a partial lift range (range which brings about a partial fit state in which the lift quantity of a valve body does not reach a full lift position because an injection pulse is short). In the partial lift range, variations in the lift quantity of the valve body (for example, needle valve) tend to increase, which hence tends to increase variations in an injection quantity. When the variations in the injection quantity are increased, there is a possibility that exhaust emission and drivability may be made worse.
In a patent document 1 (JP-T 2010-532448) is described a method for correcting variations in an injection quantity of a fuel injector. A point, which is not smooth in a time derivative of current flowing through a drive coil when a given erasing voltage is applied to the drive colt at the time of closing the fuel injector, is detected as a valve closing point, and the duration of a drive control is found on the basis of the valve closing point.
In a fuel injection control method described in a patent document 2 (WO 2004/53317), an integrated value of an actual current is calculated which flows through a coil when a drive pulse of a fuel injector is turned on and the drive pulse is corrected on the basis of the result of comparison between the integrated value of the actual current and the integrated value of a reference current.
In a plunger position detection device described in a patent document 3 JP-A 2010-73705), a convergence time required for a counter electromotive voltage developed at the time of turning off current passed through a solenoid coil to converge to a given threshold value is detected by using a fact that the inductance of a solenoid coil correlates with the position of a plunger. The inductance of the solenoid coil is calculated on the basis of the convergence time of the counter electromotive voltage. By detecting the position of the plunger on the basis of the inductance, the position of a valve body coupled to the plunger is detected.